Abstract:

An in-plane switching LCD including a plurality of gate and data lines
crossing each other to define a plurality of pixel areas; a thin film
transistor formed at a crossing of the data and gate lines; a pair of
common lines facing each other and substantially parallel to the data
lines in the pixel areas; a common electrode integrally formed with the
common lines, the common electrode being inclined by a predetermined
angle; a pair of pixel electrode lines overlapping the common lines; and
a pixel electrode integrally formed with the pixel electrode lines, the
pixel electrode being inclined substantially parallel to the common
electrode, the pixel electrode being arranged in an alternating pattern
with the common electrode, wherein the gate lines are formed
substantially parallel to the common electrode and the pixel electrode.

Claims:

1-12. (canceled)

13. A method for driving an in-plane switching liquid crystal display, the
method comprising:sequentially applying a data signal to the data lines;
andsequentially applying a scan signal to the gate lines,wherein voltages
of different polarity are alternately applied to pixel areas of a liquid
crystal panel.

14. The method according to claim 13, wherein the data signal is
sequentially applied to the data lines through a column inversion method.

15. The method according to claim 13, wherein the voltages of different
polarity are alternately applied to the pixel areas as in a dot inversion
method.

16. The method according to claim 13, wherein the voltages of different
polarity are applied to the pixel areas alternately in a vertical
direction.

17. The method according to claim 13, wherein the voltages of different
polarity are applied to the pixel areas alternately in a horizontal
direction.

Description:

[0001]This application claims the benefit of Korean Patent Application No.
2004-38854, filed on May 31, 2004, which is hereby incorporated by
reference for all purposes as if fully set forth herein,

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates to an in-plane switching (IPS) liquid
crystal display and driving method thereof. More particularly, the
present invention relates to an IPS liquid crystal display and a driving
method thereof that can provide an improved opening ratio and reduced
power consumption.

[0004]2. Discussion of the Related Art

[0005]Demand for a flat panel display device (of thin, small and
lightweight), which can be applied to a television as well as various
portable electronic devices such as a mobile phone, a personal digital
assistant (PDA), and a notebook computer, has been recently increased.
Various display devices, such as a liquid crystal display (LCD), a plasma
display panel (PDP), a field emission display (FED), and a vacuum
fluorescent display (VFD), have been actively studied for use as a flat
panel display device.

[0006]Of them, the thin, small and lightweight LCD is being spotlighted as
the flat panel display device because it can provide a high-resolution
image and low power consumption.

[0007]The LCD includes a liquid crystal panel for displaying an image, and
a driving unit for applying a driving signal to the liquid crystal panel.
The liquid crystal panel includes first and second substrates assembled
to each other, and a liquid crystal layer injected between the first and
second substrates.

[0008]Generally, the first substrate (or a TFT substrate) includes a
plurality of gate lines arranged to be spaced apart from one another by a
predetermined interval in one direction, a plurality of data lines
arranged to be respectively perpendicular to the gate lines, a plurality
of pixel electrodes arranged in a matrix shape in respective pixel areas
defined by the gate lines and the data lines, and a plurality of TFTs
turned on by signals of the gate lines to thereby transfer signals of the
data lines to the respective pixel electrodes.

[0009]The second substrate (or a color filter substrate) includes a black
matrix layer for intercepting light from portions other than the pixel
areas, an R/G/B color filter layer for reproducing color, and a common
electrode for reproducing an image. In the IPS LCD, the common electrode
is formed on the first substrate.

[0010]The first and second substrates are assembled to each other.
Thereafter, liquid crystal is injected between the assembled first and
second substrates.

[0011]Meanwhile, the LCD is driven using the optical anisotropy and
polarizability properties of liquid crystal.

[0012]The liquid crystal has directionality in a molecular arrangement
because it has a thin and long structure. The molecular arrangement
direction of the liquid crystal can be artificially controlled by
applying an electric field to the liquid crystal.

[0013]Accordingly, if the arrangement direction of the liquid crystal
molecules is changed arbitrarily, the arrangement of the liquid crystal
molecules is changed and the light polarized due to the optical
anisotropy is modulated arbitrarily. In this manner, the image
information is expressed.

[0014]The LCD has various display modes based on the arrangement of the
liquid crystal molecules. Among them, a TN LCD is widely used because it
can easily display white/black color and has a fast response speed and a
low driving voltage. In the TN LCD, when a voltage is applied, liquid
crystal molecules aligned parallel to a substrate are aligned almost
perpendicular to the substrate. Accordingly, when a voltage is applied, a
viewing angle becomes narrow due to the refractive anisotropy.

[0015]In order to solve this problem, various modes having wide viewing
angle characteristics have been proposed. Among them, an In-Plane
Switching (IPS) LCD has been developed.

[0016]When a voltage is applied, the IPS LCD forms a horizontal electric
field on the plane and aligns liquid crystal molecules on the plane,
thereby improving the viewing angle characteristic.

[0017]FIG. 1 is a sectional view of a related art IPS LCD.

[0018]In FIG. 1, a pixel electrode 12 and a common electrode 13 are formed
in the same plane on a lower substrate 11.

[0019]The lower substrate 11 is bonded with an upper substrate 15 with a
predetermined space therebetween. A liquid crystal layer 14 is formed
between the lower substrate 11 and the upper substrate 15. The liquid
crystal layer 14 operates due to a horizontal electric field formed
between the pixel electrode 12 and the common electrode 13 on the lower
electrode 11.

[0020]FIGS. 2A and 2B illustrate a change in the liquid crystal when a
voltage is on/off in the IPS LCD.

[0021]As can be seen from FIG. 2A, a phase change of the liquid crystal 14
does not occur in the off-state, i.e., when no horizontal electric field
is applied to the pixel electrode 12 or the common electrode 13. For
example, the liquid crystals are twisted at 45° from a horizontal
direction of the pixel electrode 12 and the common electrode 13.

[0022]As can be seen from FIG. 2B, a phase change of the liquid crystal
layer occurs in the on-state, i.e., when a horizontal electric field is
applied to the pixel electrode 12 or the common electrode 13. When
compared with the off-state of FIG. 2A, the twist angle is about
45° and the twist direction of the liquid crystals coincides with
the horizontal direction of the pixel electrode 12 and the common
electrode 13.

[0023]As described above, the IPS LCD has both the pixel electrode and the
common electrode on the same plane.

[0024]The IPS LCD has an advantage of a wide viewing angle. That is, when
the LCD is seen from the front, the viewing angle is at 70° in
up/down/right/left directions.

[0025]Also, compared with a general LCD, a fabricating process is simple
and a movement of color depending on the viewing angle is slight.

[0026]However, since the common electrode and the pixel electrode are
formed on the same plane, the transmission rate and the aperture ratio
are reduced.

[0027]FIG. 3 is a plan view of a related art IPS LCD.

[0028]In FIG. 3, a plurality of gate lines 32 are arranged at regular
intervals in one direction. A plurality of data lines 35 are arranged at
regular intervals in a direction perpendicular to the gate lines 32 so as
to define pixel areas P on a transparent lower substrate 31.

[0029]A common line 39 is arranged parallel to the gate lines 32 within
the pixel area P. A thin film transistor T is formed at each pixel area P
defined by the crossing of the gate line 32 and the data line 35.

[0030]Here, the thin film transistor T includes a gate electrode 32a
protruded from the gate line 32, a gate insulating layer (not shown)
formed at a front of the lower substrate 31, an active layer 34 formed on
the gate insulating layer disposed at an upper portion of the gate
electrode 32a, a source electrode 35a protruded from the data line 35,
and a drain electrode 35b spaced apart from the source electrode 35a by a
predetermined distance.

[0031]A plurality of pixel electrodes 38 are formed parallel to the data
line 35 within the pixel area P. One terminal of the pixel electrode 38
is connected to the drain electrode 35b of the thin film transistor T.
Also, a plurality of common electrodes 39a protruded from the common line
39 are formed within the pixel area P.

[0032]A shield electrode 36 is formed between the common electrodes 39a
adjacent to the data line 35 so as to prevent distortion of an electric
field.

[0033]More specifically, when a scan signal is applied to the thin film
transistor T through the gate line, the thin film transistor T is turned
on so that an image signal is input to the pixel electrode 38 through the
data line 35. Then, an electric field is formed between the common
electrode 39a and the pixel electrode 38 in a direction substantially
horizontal to the substrate. The liquid crystal molecules rotate in the
direction of the electric field.

[0034]However, when the image signal is input to the pixel electrode 38,
the electric field is formed not only between the common electrode 39a
and the pixel electrode 38 but also between the pixel electrode 38 and
the data line 35.

[0035]At this time, the electric field between the pixel electrode 38 and
the data line 35 distorts the entire horizontal electric field within the
pixel. Therefore, the liquid crystal molecules are not arranged
completely horizontal with respect to the substrate. Consequently,
crosstalk occurs in a vertical direction.

[0036]The change of the electric field effects the rotation of the liquid
crystals such that color tone is changed. In order to prevent this
problem, a shield electrode 36 for shielding the electric field is formed
between the data line 35 and the common electrode 39a and between the
data line 35 and the pixel electrode 38.

[0037]For the formation of the shield electrode 36, a width of the common
electrode 39a should be 10 μm or more.

[0038]Accordingly, as the width of the common electrode is widened due to
the formation of the shield electrode, the aperture ratio of the pixel
area is reduced.

SUMMARY OF THE INVENTION

[0039]Accordingly, the present invention is directed to an IPS liquid
crystal display and a driving method thereof that substantially obviates
one or more problems due to limitations and disadvantages of the related
art.

[0040]An advantage of the present invention is to provide an IPS liquid
crystal display and a driving method thereof, which can improve a opening
ratio by arranging a pixel electrode, a common electrode, and a gate line
to be substantially parallel to one another and to be inclined by a
predetermined angle, and can reduce power consumption by using a column
inversion method according to pixel rows.

[0041]Additional advantages and features of the invention will be set
forth in part in the description which follows and in part will become
apparent to those having ordinary skill in the art upon examination of
the following or may be learned from practice of the invention. The
objectives and other advantages of the invention may be realized and
attained by the structure particularly pointed out in the written
description and claims hereof as well as the appended drawings.

[0042]To achieve these and other advantages and in accordance with the
purpose of the invention, as embodied and broadly described herein, an
in-plane switching liquid crystal display comprising: a plurality of gate
lines and a plurality of data lines crossing each other to define a
plurality of pixel areas; a thin film transistor formed at a crossing of
the data and gate lines; a pair of common lines facing each other and
substantially parallel to the data lines in the pixel area; a common
electrode integrally formed with the common lines, the common electrode
being inclined by a predetermined angle; a pair of pixel electrode lines
overlapping the common lines; and a pixel electrode integrally formed
with the pixel electrode lines, the pixel electrode being inclined
substantially parallel to the common electrode, the pixel electrode being
arranged in an alternating pattern with the common electrode, wherein the
gate lines are formed substantially parallel to the common electrode and
the pixel electrode.

[0043]In another aspect of the present invention, there is provided a
method for driving an in-plane switching liquid crystal display, the
method including: sequentially applying a data signal to data lines; and
sequentially applying a scan signal to gate lines, wherein voltages of a
different polarity are alternately applied to pixel areas of a liquid
crystal panel.

[0044]It is to be understood that both the foregoing general description
and the following detailed description of the present invention are
exemplary and explanatory and are intended to provide further explanation
of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045]The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and constitute a
part of this application, illustrate embodiments of the invention and
together with the description serve to explain the principle of the
invention. In the drawings:

[0046]FIG. 1 is a schematic sectional view of a general IPS LCD;

[0047]FIGS. 2A and 2B are views illustrating a change of liquid crystal
when an IPC LCD is turned on or off;

[0048]FIG. 3 is a plan view of a related art IPS LCD;

[0049]FIG. 4 is a schematic plan view of an IPS LCD according to the
present invention;

[0050]FIG. 5 is an enlarged plan view of a circled-block region of a pixel
area shown in FIG. 4; and

[0051]FIG. 6 is a view illustrating a case where a pixel row of an
inventive IPS LCD is driven when a signal is applied to the pixel row.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0052]Reference will now be made in detail to embodiments of the present
invention, examples of which are illustrated in the accompanying
drawings. Wherever possible, the same reference numbers will be used
throughout the drawings to refer to the same or like parts.

[0053]FIG. 4 is a schematic plan view of an IPS LCD according to the
present invention, and FIG. 5 is an enlarged plan view of a circled block
region of a pixel area shown in FIG. 4.

[0054]In FIGS. 4 and 5, in order to define pixel areas in an IPS LCD of
the present invention, a plurality of vertical data lines 44 are spaced
apart from one another by a predetermined interval, and a plurality of
gate lines 42 are arranged to be inclined by a predetermined angle with
respect to the data lines 44.

[0055]A TFT "T" is formed in respective pixel areas P1 to P4 defined by
crossings of the data lines 44 and the gate lines 42. The TFT maybe
disposed at a left or right side of the pixel area according to pixel
columns.

[0056]That is, source electrodes 45A connected to one data line 44 are
alternately provided in right and left pixel areas with respect to the
data line 44.

[0057]Also, a common line 51 and a pixel electrode line 52 are arranged
substantially parallel to the data line 44 at a position neighboring the
data line 44 in the pixel area. The common line 51 and the pixel
electrode line 52 are formed to have a width of about 8 μm or below.

[0058]Also, the common line 51 and the pixel electrode line 52 overlap
with each other and thus forms a storage capacitance in each pixel area.

[0059]First and second electrodes protrude from the common line 51 and the
pixel electrode line 52, and are arranged substantially parallel to the
gate line 42. The first electrode and the second electrode correspond
respectively to a common electrode 46 and a pixel electrode 48.

[0060]The common electrode 46 and the pixel electrode 48 maybe inclined
upward or downward with respect to a horizontal center line of the pixel
area, whereby a wide viewing angle can be achieved.

[0061]In addition, the gate line 42 is are arranged substantially parallel
to the common electrode 46 and the pixel electrode 48, whereby an opening
ratio is improved.

[0062]In FIG. 5, the TFT includes a gate electrode (not shown) extended
from the gate line 42, a semiconductor layer (not shown) formed on the
gate electrode, a source electrode 45A formed on the semiconductor layer
and extended from the data line 44, and a drain electrode 45B. A scan
signal is applied to the gate electrode and the semiconductor layer is
activated by the scan signal to thereby form a channel layer. An image
signal is applied to the source electrode 45A.

[0063]The common electrode 46 and the pixel electrode 48 are arranged to
incline by a predetermined angle with respect to a horizontal direction
substantially perpendicular to the data line 44, and the gate line 42 is
arranged substantially parallel to the common electrode 46 and the pixel
electrode 48. Here, the inclination angle is below about 45°.

[0064]When the common electrode 46, the pixel electrode 48, and the gate
line 42 are arranged to incline as above, liquid crystal can be aligned
horizontally (0°).

[0065]Since the direction of an electric field generated between the data
line 44 and the neighboring common electrode 46 is identical to the
alignment direction of the liquid crystal, a distortion is not generated
due to an electric field generated from the data line 44.

[0066]Accordingly, an opening ratio of the pixel area can be improved
because a separate shield electrode and a black matrix for shielding an
undesirable electric field are unnecessary.

[0067]Also, when the gate line 42 is not perpendicular to the data line 44
but is arranged to be inclined by a predetermined angle with respect to
the horizontal direction, the opening ratio can be improved because the
interval between the gate line 42 and the neighboring pixel electrode 48
can be maintained at a constant value (for example about 10 μm).

[0068]When the pixel electrode 48 and the common electrode 46 are arranged
to be inclined and the gate line 42 is horizontally arranged, an interval
between the gate line 42 and the pixel electrode 48 is not constantly
maintained.

[0069]Accordingly, a region where the above interval is above about 10
μm exists in one pixel area. Since such an undesirable region cannot
be used as a region for effectively transmitting light, the opening ratio
is reduced.

[0070]However, the gate line 42 is arranged substantially parallel to the
pixel electrode 48 and the common electrode 46 in the present invention.
That is, an interval between the gate line 42 and the pixel electrode 48
is constantly maintained. Accordingly, since a region where the above
interval is above about 10 μm does not exist in one pixel area, the
opening ratio can be improved.

[0071]Here, the above interval is not limited to about 10 μm, but may
be varied according the size and image resolution of a liquid crystal
panel.

[0072]Also, since the gate line 42 is symmetrically inclined with respect
to the front gate line 42, an opening region of the pixel area can be
further widen.

[0073]Meanwhile, the common electrode 46 is connected to the common line
51 arranged near the neighboring pixel, and the pixel electrode 48 is
connected to the pixel electrode line 52 overlapping with the common line
51.

[0074]The common line 51 and the pixel electrode line overlap with each
other to thereby form a storage capacitor for use as a storage electrode.

[0075]The storage capacitor 50 is used to improve the retention property
of a voltage applied to liquid crystal and stability in gradation
reproduction, and to reduce a flicker and an afterimage.

[0076]FIG. 6 is a view illustrating a pixel row of an inventive IPS LCD
driven when a signal is applied to the pixel row.

[0077]In FIG. 6, a TFT formed at a portion where the gate line and the
data line cross each other may be arranged at the left or right side of a
pixel area according to pixel columns.

[0078]In detail, since the TFT may be arranged at the left or right side
of a corresponding pixel area according to pixel columns, each TFT
receives a signal according to the polarity applied thereto.

[0079]When data signals are sequentially applied to the first and second
data lines according to a column inversion method, a data signal is
applied to each pixel area connected to a source electrode of the first
data line (See a pixel structure in FIG. 4).

[0080]Since two data lines can apply data signals respectively to pixel
areas formed along one column in a zigzag pattern, the pixel areas
corresponding to a vertical direction of the data lines is alternately
turned on/off.

[0081]A turned-off pixel area is turned on by a data signal supplied from
the neighboring data line.

[0082]Accordingly, as shown in FIG. 6, pixel areas driven by a column
inversion method are driven as in a dot inversion method.

[0083]When data signals are sequentially applied to two data lines and
on/off signals are sequentially applied to gate lines, a voltage higher
than that of a common electrode is applied to a pixel area P1 connected
to the first data line, and a voltage lower than that of the common
electrode is applied to a neighboring pixel area P2 because a data signal
is not applied thereto.

[0084]Likewise, when an on/off driving signal is applied to the next gate
line, a voltage lower than that of the common electrode is applied to the
pixel area P2 because a data signal is not applied thereto, and a voltage
higher than that of the common electrode is applied to the pixel area P4
because a data signal is applied thereto.

[0085]As described above, in the inventive IPS LCD, the pixel electrode,
the common electrode, and the gate line are arranged substantially
parallel to one another, whereby an opening ratio can be improved.

[0086]Also, a dot inversion method may be implemented using a column
inversion method where a TFT is disposed at a left or right side of a
pixel area according to pixel columns, whereby power consumption can be
reduced.

[0087]It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention without
departing from the spirit or scope of the invention. Thus, it is intended
that the present invention covers the modifications and variations of
this invention provided they come within the scope of the appended claims
and their equivalents.